Artificial vertebral disk replacement implant with translating pivot point and method

ABSTRACT

An artificial vertebral disk replacement implant is disclosed along with its method of operation and a method of implanting. The implant has first and second plates that each mate with a vertebral body. Each plate has one side for mating with a vertebral body. The first plate has a socket on one side, and the second plate has an elongated ball on one side. The ball of the first plate and the socket of the second plate form a ball-and-socket joint when the two plates are in contact with each other. The implant achieves a range of motion equivalent to a natural range of motion.

CLAIM OF PRIORITY

[0001] This application claims priority to U.S. Provisional ApplicationNo. 60/422,039, filed on Oct. 29, 2002, entitled “ARTIFICIAL VERTEBRALDISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT AND METHOD,”(Attorney Docket No. KLYCD-05007US0) and which is incorporated herein byreference.

CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application is related to U.S. Provisional Application No.60/422,021, filed on Oct. 29, 2002, entitled “TOOLS FOR IMPLANTING ANARTIFICIAL VERTEBRAL DISK AND METHOD” (Attorney Docket No.KLYCD-05008US0), U.S. patent application Ser. No. 10/___,___, filed Oct.14, 2003, entitled “TOOLS FOR IMPLANTING AN ARTIFICIAL VERTEBRAL DISKAND METHOD” (Attorney Docket No.: KLYCD-05008US1), U.S. ProvisionalApplication No. 60/422,011, filed Oct. 29, 2002, entitled “ARTIFICIALVERTEBRAL DISK REPLACEMENT IMPLANT WITH CROSSBAR SPACER AND METHOD”(Attorney Docket No. KLYCD-05009US0), U.S. patent application Ser. No.10/___,___, filed Oct. 14, 2003, entitled “ARTIFICIAL VERTEBRAL DISKREPLACEMENT IMPLANT WITH CROSSBAR SPACER AND METHOD” (Attorney DocketNo. KLYCD-05009US1), U.S. Provisional Application No. 60/422,022, filedOct. 29, 2002, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANTWITH SPACER AND METHOD,” (Attorney Docket No. KLYCD-05010US0), and U.S.patent application Ser. No. 10/___,___, filed Oct. 14, 2003, entitled“ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH SPACER AND METHOD,”(Attorney Docket No.: KLYCD-05010US1), which are incorporated herein byreference.

FIELD OF THE INVENTION

[0003] This invention relates to an artificial vertebral diskreplacement, a method of operation, and a method of implanting.

BACKGROUND OF THE INVENTION

[0004] As the present society ages, it is anticipated that there will bean increase in degenerative and dysfunctional spinal disk conditions.Pain associated with such disk conditions can be relieved by medicationand/or surgery.

[0005] Over the years, a variety of intervertebral implants have beendeveloped in an effort to relieve the pain associated with suchdegenerative and dysfunctional disk conditions. For example, U.S. Pat.No. 4,349,921 to Kuntz discloses an intervertebral disk prosthesis. TheKuntz prosthesis is designed to restore the space between the disks.

[0006] U.S. Pat. No. 4,714,469 to Kenna discloses a spinal implant thatfuses vertebrae to the implant. The implant has a rigid body that fitsbetween the vertebrae with a protuberance extending from a vertebralcontacting surface and into the vertebral body.

[0007] U.S. Pat. No. 5,258,031 to Salib et al. discloses anotherprosthetic disk with a ball that fits into a socket.

[0008] U.S. Pat. Nos. 5,425,773 and 5,562,738 are related patents toBoyd et al. that disclose a disk arthroplasty device for replacement ofthe spinal disk. A ball-and-socket are provided to enable rotation.

[0009] U.S. Pat. No. 5,534,029 to Shima discloses an articulatedvertebral body spacer with a pair of upper and lower joint piecesinserted between the vertebrae. An intermediate layer is provided toallow for movement between the upper joint piece and the lower jointpiece.

[0010] U.S. Pat. No. 5,782,832 to Larsen et al. discloses a two-pieceball-and-socket spinal implant with upper and lower plates for insertionwithin the intervertebral space.

[0011] U.S. Pat. No. 6,156,067 to Bryan et al. discloses a prosthesishaving two plates with a nucleus therebetween.

[0012] None of these solutions provide an implant that restores a widerange of natural movement.

[0013] Accordingly, what is needed is an implant for alleviating suchconditions and that restores natural movement.

SUMMARY OF THE INVENTION

[0014] The present invention includes embodiments that are directed toan implant for alleviating discomfort associated with the spinal column.One embodiment of the implant includes a first plate with an elongatedsocket and a second plate that mates with the first plate and has anelongated ball. The implant is designed to replace the disk between twovertebrae.

[0015] Other aspects, objects, features, and elements of the otherembodiments of the invention are described or are evident from theaccompanying specification, claims and figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1A is a posterior view of an embodiment of the assembledimplant of the invention. FIG. 1B is a cross-section of the device shownin FIG. 1A. FIG. 1C is a posterior view of two bottom plates of theimplant of the embodiment of the invention. FIGS. 1D and 1E areposterior views of the embodiment of the implant of the invention shownin FIG. 1A illustrating the operation of the device in bending to theleft and bending to the right, respectively.

[0017]FIG. 2A is a side view of the implant of FIG. 1A showing theimplant in flexion. FIG. 2B is a side view of the implant showing theimplant in extension. FIG. 2C is a partial cross-sectional view of aside view of the implant of an embodiment of the invention. FIG. 2D is apartial cross-sectional view of an alternative embodiment of the implantof the invention having a protuberance adjacent the socket.

[0018]FIG. 3A is a top view of a portion of an embodiment of theassembled implant of the invention. FIG. 3B is a top view of anembodiment of the implant of the invention showing a rotation to theright. FIG. 3C is a top view of an embodiment of the implant of theinvention showing a rotation to the left.

[0019]FIG. 4A is a perspective view of a ball portion of the embodimentof the implant of the invention. FIG. 4B is a perspective view of asocket portion of the embodiment of the implant of the invention.

[0020]FIG. 5A is a posterior view of the embodiment of the implant ofthe invention after being implanted between two vertebral bodies. FIG.5B is a side view of the embodiment of the implant of the inventionafter being implanted between two vertebral bodies.

[0021]FIG. 6 is a rear view of an alternate embodiment of the inventionhaving two plates.

[0022]FIG. 7A is a top view of an embodiment of a cutting tool of theinvention used to prepare the vertebral bodies for the implant. FIG. 7Bis a side view of the embodiment of the cutting tool of the inventionfrom the distal end. FIG. 7C is a distal end view of an embodiment ofthe cutting tool of the invention. FIG. 7D is a top view of the cuttingportion of an alternative embodiment of the cutting tool of theinvention showing blade protectors. FIG. 7E is a side view of thecutting portion of an alternative embodiment of the cutting tool of theinvention showing the blade protectors.

[0023]FIG. 8A is a side view of an embodiment of the implant insertiontool of the invention. FIG. 8B is a top view of the embodiment of theimplant insertion tool of the invention. FIG. 8C is a distal end view ofthe embodiment of the implant insertion tool of the invention. FIG. 8Dis a top view of an embodiment of the implant insertion tool holding anembodiment of the implant.

[0024]FIG. 9 is a block diagram illustrating the steps of a method forinserting the implant between vertebral bodies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0025] The following description is presented to enable any personskilled in the art to make and use the invention. Various modificationsto the embodiments described will be readily apparent to those skilledin the art, and the principles defined herein can be applied to otherembodiments and applications without departing from the spirit and scopeof the present invention as defined by the appended claims. Thus, thepresent invention is not intended to be limited to the embodimentsshown, but is to be accorded the widest scope consistent with theprinciples and features disclosed herein. To the extent necessary toachieve a complete understanding of the invention disclosed, thespecification and drawings of all patents, patent publications, andpatent applications cited in this application are incorporated herein byreference.

[0026] Turning now to FIG. 1A, a posterior view of an intervertebralimplant 100 is depicted having a four-piece configuration. Although, aswill be appreciated by those of skill in the art, other configurations,such as a two-piece configuration or a three-piece configuration, arepossible without departing from the scope of the invention. As depicted,the intervertebral implant 100 has a pair 130 of first plates 110. Eachfirst plate 110 has a first surface 112 and a second surface 114. Thefirst surface 112 is configured to abut an end plate surface of avertebral body. A keel 116 can be provided on the first surface 112 toanchor the first surface 112 into the vertebral body upon implantation.One or more additional protrusions 118 can also be provided that act asa detent or catch, thus providing a further mechanism to prevent thefirst plate 110 from moving relative to the vertebral body onceimplanted.

[0027] The intervertebral implant 100 also has a pair 132 of secondplates 120. The second plates 120 have a first surface 122 and a secondsurface 124. The first surface 122 is configured to abut an end platesurface of a vertebral body. As with the first plate 110, a keel 126 canbe provided on the first surface 122 to anchor the first surface 122into the vertebral body upon implantation. One or more additionalprotrusions 128 can also be provided that act as a detent or catch,again providing a further mechanism to prevent the second plate 120 frommoving relative to the vertebral body once implanted.

[0028]FIG. 1B depicts the pair 130 of upper plates 110 and the pair 132of lower plates 120 in cross-section. Each upper plate 110 has a socket136 that has a first elongated sidewall 150, a corresponding secondelongated sidewall 152 (shown in FIG. 3B), an end wall 154, and an openend 156. The open ends 156 of each of the first plates 110 are orientedso that the open ends 156 face each other. The lower plates 120 eachhave a ball 134. As illustrated in FIG. 1B, the ball 134 is an elongatedball. Each of the plates 110, 120 has a first end 138, 141 and a secondend 139, 143, respectively. The ends 139 of the first plate 110 faceeach other and the ends 143 of the second plate 120 also face eachother. The ends 138, 141 are curved and convex, as shown in FIG. 3A, sothat the implant 100 has a configuration that correlates to the curvedshape of a vertebra.

[0029] As shown in FIG. 1C, the ball 134 has four sides: a firstelongated sidewall 140, a second elongated sidewall 142, a third endwall 143, and a fourth end wall 146. The third end wall 144 is flushwith the end 143 of the plate 120 of the implant. The third end wall 144has a profile height 160 and the fourth end wall 146 has a profileheight 162. Comparing the profile heights 160, 162 to each other at thesame point on the second surface 124 of the second plate 120, theoverall profile height of the third end wall 144 is greater than thefourth end wall 146 (i.e., 160>162). Thus, it is evident that the uppersurface 135 of socket 136 slopes downwardly from the end wall 144 to theend wall 146. Together balls 134 comprise a ball structure that has ahigh surface where the third end walls 144 abut each other and slope toa lower surface adjacent to fourth end walls 146. Also, preferably, theupper surfaces 135 are barrel shaped and have a “U” shaped profile alonga cross-section that is perpendicular to the page of FIG. 1C (parallelthe sagittal plane on implantation). The sloping upper surface 135, aswill be explained later, allows the pair 130 of upper plates 110 toeasily slide, or rock, side-to-side on the ball structure and slide, orride, forward and backward with enough looseness of fit to allow forsome twisting in order to emulate the motion of the vertebral bone andintervertebral disk tissue. This arrangement, thus, has a sliding ortranslating pivot point. Further, as indicated in FIG. 1C the edges areeased or rounded to allow for further range of motion of the pair 130 ofplates 110 relative to the pair 132 of plates 120. As will beappreciated by those of skill in the art, the overall height of thethird end wall 144 and the fourth end wall 146 can be equivalent whilestill having an effective third end wall height 160 that is greater thanthe effective fourth end wall height 162 due to the overall slope of thesecond surface 124. Alternatively, the overall height of the third endwall 144 and the fourth end wall 146, can be different with the thirdend wall 144 having a height greater than the fourth end wall 146, thuseliminating the need for the second surface 124 to have a slope orfurther increasing the net difference between the height of the thirdend wall and the fourth end wall.

[0030] Further, although the ball 134 is depicted such that the thirdend wall 144 is flush with the second end 143, those of skill in the artwill appreciate that the ball 134 could also be configured such that thethird end wall 144 was recessed relative to the end 143 of the secondplate. In such a configuration, the third end wall 144 and the end 143would not be flush.

[0031]FIGS. 1D and 1E illustrate posterior views of the implant 100showing the clearance for left and right lateral bending. Typically,left and right lateral bending ranges from 3-5°. As evident from thesefigures (and FIG. 1B), the length L1 of the ball 134 can be less thanthe length L2 of the socket 136. Further, as shown, the open ends 156 ofthe sockets facilitate movement of the balls 134 within the socket 136to accommodate side-bending movement.

[0032]FIG. 2A is a side view of the intervertebral implant 100. Thefirst plate 110 with this socket 136 and the second plate 120 with theball portion 134 are depicted. As is apparent from the figure, thesloping of the second surface 114 of the first plate 110 facilitatesrotation of the ball-and-socket joint in an anterior “A” 280 directionand a posterior “P” 282 direction. As depicted, the second surface 114slopes from a high point at about where the socket is located to lowpoints at the ends 111 and 113 of the plate 110. As shown in FIG. 2A,the implant 100 is positioned to achieve flexion 272 (i.e., forwardbending) in a range up to about 15°, but more preferably 10°.

[0033] As shown in FIG. 2A the second plate 120 can also have channels264, 265 or a groove adjacent the ball 134. The channels 264, 265 can beconfigured such that it surrounds a portion of the ball 134 or theentire ball 134. As will be explained below, the channel allows thesides of the ball 134 to be made more perpendicular so as to create agreater blocking wall thus preventing the socket of the upper plate 100from moving too much anteriorly or posteriorly relative to the lowerplate 120.

[0034] Either one or both of the keels on the first surface 116 and thesecond surface 126 can have one or more posteriorly pointing teeth 266to enable it to more securely engage the vertebral body into which it isimplanted. As can be seen in FIG. 2A, the protrusions 128, as well asthe additional protrusions 118 (FIG. 1A) can also have posteriorlypointing teeth in order to lock the implant 100 in position in thevertebrae.

[0035]FIG. 2B is an alternate side view of the intervertebral implant100 wherein the plates 110, 120 are shown and the ball-and-socket jointis positioned to achieve extension 274 (i.e., backward bending) in apreferable range of up to about 5°.

[0036]FIG. 2C is a cross-section of the side view of the intervertebralimplant 100 showing the mating of the ball 134 to the socket 136. FIG.2D illustrates an alternate embodiment of the first plate 110 whereinthe socket 136 has ridges 268, 269 forming a protuberance that extendsinto the channel 264, 265 respectively on the second plate 120. As willbe appreciated by those of skill in the art, the protuberances 268, 269can extend partially into the channel, such as the configuration shown,or can have a channel conforming shape such that when theball-and-socket joint are moved to achieve flexion 272 or extension 274the protuberance or ridge 268, 269 extends into the channels 264, 265.This embodiment allows the surfaces 114 and 115 of the first plate 110and the second plate 115 to be flat and non-sloping as shown while stillallowing for the implant to emulate forward and backward bending andallow for the blocking of the motion of the socket relative to the ball.

[0037] Turning now to FIG. 3A, a top view of one-half of theintervertebral implant 100 is shown. Each of the top first plate 110 andthe bottom second plate 120 have a bore 376 for receiving a pin of animplant tool. The keel 116 on the first plate 110 is positioned so thatit is does not align in the same plane with the keel 126 on the secondplate 120. As will be explained in further detail later, thenon-alignment allows for the implant including the keels to be properlypositioned between the vertebrae in such a way to accommodate theposition of the nerves as the nerves extend out from the betweenadjacent vertebrae. Additionally, the length of ball 134 from the thirdend wall 144 to the fourth end wall 146 is shorter than the length ofthe socket 136 from the end wall 154 to the open end 156 as discussedbefore.

[0038]FIGS. 3B and 3C show the relative rotation of the upper firstplate 110 to the lower second plate 120 to achieve rotation about acentral axis 378. This rotation results in about a 3°-6° rotation aboutthe axis (i.e., 3° of torso twisting in each direction).

[0039]FIG. 4A shows a perspective view of a second plate 120 of theintervertebral implant 100. The second surface 124 of the second plate120 with the ball 134 and channels or grooves 264, 265 extendingthereabout. As illustrated in FIG. 4A, the channels 264, 265 are formedon two sides of the ball 134. However, as will be appreciated by thoseof skill in the art, the channels 264, 265 can alternatively surroundthe ball 134.

[0040]FIG. 4B shows a perspective view of the first plate 110. The firstplate 110 has a second surface 114, as described above, and, extendingtherefrom is the socket 136 therein. The socket 136 of FIG. 4B isconfigured to mate with the ball 134 of FIG. 4A, as described above.

[0041]FIG. 5A illustrates a posterior view of the implant shown in FIG.1A implanted between vertebral bodies in a spine. FIG. 5A illustratesthe spinal column 500 and the cauda equina 504 (a collection of lumbarand sacral nerve roots that fill the caudal end of the spinal cord) withindividual nerves 506 exiting the cord between lumbar vertebrae. Theimplant 100 is positioned between two vertebral bodies 520, 521 suchthat the keels 116, 126 do not interfere with the cauda equina 504 andthe exiting nerve 506. As can be seen in FIG. 5A, the keel 116 of theupper first plates 110 are close together and inboard of the keel 126 ofthe lower second plate 120. This allows the lower keels 126 to be clearof the nerves 506 as the nerves exit from between the adjacentvertebrae.

[0042]FIG. 5B illustrates a side view of the implant 100, such as thatshown in FIG. 1A, implanted between vertebral bodies 520, 521. Theimplant 100 is implanted so that the ball-and-socket joint enables abouta 5° extension (backward bending) and about a 10° flexion (forwardbending). In this view, the ball and socket arrangement crosses thecenterline 50 of the implant 100 and extends in a posterior 282direction. In this embodiment, the ball-and-socket arrangement can bemore centered on the centerline 50 or extend from a position when theimplant 100 crosses the centerline 50 and extends in an anterior 280direction. Further, in another preferred embodiment, the ball can beapproximately bisected by the centerline.

[0043]FIG. 6 illustrates a rear view of an alternate embodiment of theimplant shown in FIG. 1A. The implant 600 of FIG. 6 is in the form of atwo-piece implant 600 having a first plate 610 and a second plate 620.The first plate 610 has a first surface 612 that contacts the vertebralbody and has one or more keels 616 and detents 618 for anchoring thefirst plate 610 into the vertebral body. The implant 600 also has asecond plate 620 that has a first surface 622 that contacts thevertebral body and has one or more keels 626 and detents 628 foranchoring the second plate 620 into the vertebral body. The secondsurface 614 of the first plate 610 has a socket 632 formed therein whilethe second surface 624 of the second plate 620 has a ball 630. Thisimplant 600 moves in much the same way as implant 100 described above.

[0044] As will be appreciated by those of skill in the art, implant 100is predominantly designed for a posterior implantation method. However,implant 100 can also be implanted from an anterior direction. Implant600 is designed for predominantly an anterior implantation approach.

[0045] Further, a combination of the two embodiments shown in FIG. 1Aand FIG. 6 can be used to create a three-piece implant as will also beappreciated by those of skill in the art. For example, the first plate610 of FIG. 6 with its socket 632 can be combined with two-second plates120 of FIG. 1A to form an implant. Similarly, the second plate 620 ofFIG. 6 and its ball 630 can be combined with two first plates 110 fromFIG. 1A to achieve an implant. Neither of these configurations departfrom the scope of the invention. It is also to be understood that theimplant 100, 600 can be comprised of any suitable biocompatiblematerial, such as titanium.

[0046] Turning now to FIGS. 7 and 8 and the tools for preparing thevertebral bodies and implanting the implant 100 as described. FIG. 7Adepicts a top view of a cutting tool 700 used to prepare the vertebralbodies for the implant 100 and FIG. 7B depicts a side view of tool 700.The cutting tool 700 has a handle 710 at its proximal end forcontrolling the tool during operation. As will be appreciated by thoseof skill in the art, the handle 710 can be removable or affixed to thecutting end.

[0047] The distal end 702 of the tool 700 is forked to form two prongsor tines 705, 706. The end of each tine 705, 706 has a beveled edge 716at its distal most end. Each tine 705, 706 also has an inner blade 712located on an inner upper side and an outer blade 714 located on anouter lower side (shown in FIG. 7C). Preferably the inner blades 712 arecoplanar with the surface of the inner side of the tine and the outerblades 714 are coplanar with the outer side of the tine. The innerblades 712 are oriented to cut a space in a first intervertebral bodyfor the first surface keel 116 of the implant and the outer blades 714are oriented to cut a space in the facing intervertebral body for thesecond surface keel 126. The orientation of the blades is such that eachof the cuts made for the keels of the implant are offset and avoid thenerves in the cauda equina or exiting the cauda equina.

[0048]FIG. 7C is a view of the distal end of the cutting tool 700showing the beveled edges 716 of the tines 705, 706 and the inner blades712 and outer blades 714. The distance 722 between the inner blades 712is less than the distance 724 between the outer blades and the height hof the tines approximates the distance between two vertebral bodies orthe height of the disk space. The blades 712, 714 extend above and belowthe tines or the height of the tines. As can be seen in FIG. 7C, thebeveled sides of the distal end 716 extend and form at least one of thebeveled sides of the blades 712, 714.

[0049]FIG. 7D depicts an enlarged top view of the tines 705, 706 of thedistal end of cutting tool 700 with the beveled distal edges 716. FIG.7E is an enlarged side view of the distal end of cutting tool 700. FIGS.7D and 7E show the retractable blade protector 720 for the blade 712positioned in a retracted position. As the cutting tool is insertedbetween vertebral bodies, the retractable blade protector 720 moves in aposterior direction 715 (i.e., toward the handle 710) to expose theinner blade 712 and the outer blade 714 and to enable the blades to cutinto the vertebral bodies. These protectors 720 can be spring biased asdesired in order to cover the blade 712, 714 as the tool 700 is insertedpast the nerves. The protectors 720 are urged in a posterior directionas the blades 712, 714 are urged into the vertebral bodies in order tocut channels for the keels. Springs 721 provide the desired bias to keepthe protectors 720 in a forward position covering the blades 712, 718.

[0050] As will be appreciated by those of skill in the art, the toolshown in FIG. 7 can be modified such that instead of cuttingkeel-receiving channels in the upper and lower vertebral bodies at thesame time, two tools are provided so that only one vertebral body is cutfor keel-receiving channels at a time. For example, a first tool havingtwo tines as described above could be provided having a pair of innerblades located on an upper surface of the tines. A second tool could beprovided having tines as described with a pair of outer blades locatedon the lower surface of the tines. Optionally, the second tool can havea guide corresponding to the location of the first blade on the firsttool to ensure that the second cut is optimally aligned with the firstcut. In use, a pair of channels can be cut into the upper vertebral bodyusing the first tool. Thereafter a second pair of channels can be cutinto the lower vertebral body. Alternate arrangements are also possible,for example, where the first tool has a pair of outer blades and thesecond tool has a pair of inner blades, or where the first tool hasupper and lower blades on a first tine (e.g., right tine) and the secondtool has upper and lower blades on a second tine (e.g., left tine).

[0051]FIG. 8A depicts the implanting tool used to insert the implant 100of FIG. 1A between vertebral bodies. FIG. 8A is a side view of theimplantation tool 800 that has a handle 810 and an implant holder 820.The implant holder 820 has an implant conforming surface 824 and twopins 822 for holding a first plate 110 and a second plate 120 of a firsthalf of the implant 100. The conforming surface 824 is curved to followthe convex outer edges 138, 139 of the plate 100, 120, respectively(shown in FIG. 3A). The implant 100 nests within a conforming surface824 and is held by pins 822. FIG. 8C shows the distal view of the end ofthe tool with two pins 822, 823 for securing the first and second plateof the implant. The tool can be rotated by the user 180° to implant theother half of the implant.

[0052] Where an implant such as that shown in FIG. 6 is implanted, theimplant conforming surface 824 of the implant tool would have a mirrorimage conforming surface provided to capture the implant 600. Anadditional series of pins, for a total of four, can be provided forholding a first plate 610 and a second plate 620 of the implant 600, ifrequired. The implant 600 would nest within the conforming surface ofthe “U” shaped cavity.

[0053] A variety of kits can be assembled that include an implant 100(or 600) sized for a particular patient. The kit could also includeseveral cutting tools 700 and several implanting tools 800 or a singlehandle that cooperates with cutting ends 702 and implantation ends 820.

[0054]FIG. 9 is a block diagram showing the steps for implanting animplant. In order to implant the implant of FIG. 1A, the spine isexposed posteriorly 910. The intervertebral disk to be replaced iseither partially or completely removed 920. The cutting tool 700 isinserted between the vertebral bodies to create channels in the bodiesto receive the keels of the implant. Nerves can be retracted and thenthe implant holder 810 is used to insert the implant between thevertebral bodies 930, lining the keels up with the channels created bythe cutting tool 700. Next, the nerves are retracted in the otherdirection and the other plates 100, 120 are attached to a tool and areimplanted. The implant first and second plates 110, 120 are now insertedbetween the vertebrae, and the keel are placed in the channels preparedby the cutting tool 700. Once the implant is inserted, the wound isclosed 940.

[0055] In order to implant the implant of FIG. 6, the spine is exposedanteriorly 910. The intervertebral disk to be replaced is eitherpartially or completely removed 920. The cutting tool 700 is insertedbetween the vertebral bodies to create channels in the bodies to receivethe keels of the implant. The implant is then inserted into an implantholder and the implant tool is used to insert the implant between thevertebral bodies 930, lining the keels up with the channels created bythe cutting tool 700. Once the implant is inserted, the wound is closed940.

[0056] The foregoing description of embodiments of the present inventionhas been provided for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications and variations will beapparent to the practitioner skilled in the art. The embodiments werechosen and described in order to best explain the principles of theinvention and its practical application, thereby enabling others skilledin the art to understand the invention and the various embodiments andwith various modifications that are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the following claims and their equivalence.

What is claimed:
 1. An intervertebral implant comprising: a first plateadapted to mate to a first vertebral body, the first plate including anelongated socket; a second plate adapted to mate to a second vertebralbody, the second plate including an elongated ball, with the elongatedball having a top surface and first and second elongated sidewalls thatare substantially perpendicular to the second plate, and third andfourth end walls; and the top surface slopes from the third end wall tothe fourth end wall.
 2. The implant of claim 1 wherein: the third endwall has a height that is greater than a height of the fourth end wall.3. The implant of claim 1 wherein: the socket has first and secondelongated sidewalls, an end wall, and an open end.
 4. The implant ofclaim 1 including at least one of the first and second plates includinga keel extending therefrom and adapted to engage a vertebral body. 5.The implant of claim 1 including a first keel extending from the firstplate and adapted to engage a first vertebral body, and a second keelextending from the second plate and adapted to engage a second vertebralbody.
 6. The implant of claim 1 including a first keel extending fromthe first plate and substantially perpendicular to the elongated socketand adapted to engage a first vertebral body, and a second keelextending from the second plate and substantially perpendicular to theelongated ball and adapted to engage a second vertebral body.
 7. Theimplant of claim 1 wherein the elongated socket has first and secondsidewalls that are substantially perpendicular to the first plate. 8.The implant of claim 1 wherein the third end wall and the fourth endwall are substantially perpendicular to the second plate.
 9. Anintervertebral implant comprising: a first plate adapted to mate to afirst vertebral body, the first plate including an elongated socket; asecond plate adapted to mate to a second vertebral body, the secondplate including an elongated ball, with the elongated ball having a topsurface and first and second elongated sidewalls, and third and fourthend walls; and the top surface slopes from the third end wall to thefourth end wall.
 10. The implant of claim 9 wherein: the third end wallhas a height that is greater than a height of the fourth end wall. 11.The implant of claim 9 wherein: the socket has first and secondelongated sidewalls, an end wall, and an open end.
 12. The implant ofclaim 1 including at least one of the first and second plates includinga keel extending therefrom and adapted to engage a vertebral body. 13.The implant of claim 9 including a first keel extending from the firstplate and adapted to engage a first vertebral body, and a second keelextending from the second plate and adapted to engage a second vertebralbody.
 14. The implant of claim 9 including a first keel extending fromthe first plate and substantially perpendicular to the elongated socketand adapted to engage a first vertebral body, and a second keelextending from the second plate and substantially perpendicular to theelongated ball and adapted to engage a second vertebral body.
 15. Theimplant of claim 9 wherein the socket has first and second elongatedsidewalls that are substantially perpendicular to the first plate. 16.The implant of claim 9 wherein the third end wall and the fourth endwall are substantially perpendicular to the second plate.
 17. Anintervertebral implant comprising: a first plate adapted to mate to afirst vertebral body, the first plate including a socket; a second plateadapted to mate to a second vertebral body, the second plate includingan elongated ball, with the elongated ball having a top surface andfirst and second elongated sidewalls that are substantiallyperpendicular to the second plate, and third and fourth end walls; andthe top surface of the elongated ball has a location between the thirdend wall and the fourth end wall with a height that is greater than aheight of the third end wall and a height of the fourth end wall, andwherein the top surface slopes toward the third end wall and toward thefourth end wall.
 18. The implant of claim 17 wherein: the socket hasfirst and second elongated sidewalls, an end wall, and an open end. 19.The implant of claim 17 including at least one of the first and secondplates including a keel extending therefrom and adapted to engage avertebral body.
 20. The implant of claim 17 including a first keelextending from the first plate and adapted to engage a first vertebralbody, and a second keel extending from the second plate and adapted toengage a second vertebral body.
 21. The implant of claim 17 including afirst keel extending from the first plate and substantiallyperpendicular to the elongated socket and adapted to engage a firstvertebral body, and a second keel extending from the second plate andsubstantially perpendicular to the elongated ball and adapted to engagea second vertebral body.
 22. The implant of claim 17 wherein the firstand second sidewalls of the socket are substantially perpendicular tothe first plate.
 23. The implant of claim 17 wherein the third end walland the fourth end wall are substantially perpendicular to the secondplate.
 24. An intervertebral implant comprising: a first plate adaptedto mate to a first vertebral body, the first plate including a socket; asecond plate adapted to mate to a second vertebral body, the secondplate including an elongated ball, with the elongated ball having a topsurface and first and second elongated sidewalls, and third and fourthend walls; and the top surface has a location between the third end walland the fourth end wall with a height that is greater than a height ofthe third end wall and a height of the fourth end wall, and the topsurface slopes to the third end wall and to the fourth end wall.
 25. Theimplant of claim 24 wherein: the socket has first and second elongatedsidewalls, an end wall, and an open end.
 26. The implant of claim 24including at least one of the first and second plates including a keelextending therefrom and adapted to engage a vertebral body.
 27. Theimplant of claim 24 including a first keel extending from the firstplate and adapted to engage a first vertebral body, and a second keelextending from the second plate and adapted to engage a second vertebralbody.
 28. The implant of claim 24 including a first keel extending fromthe first plate and substantially perpendicular to the elongated socketand adapted to engage a first vertebral body, and a second keelextending from the second plate and substantially perpendicular to theelongated ball and adapted to engage a second vertebral body.
 29. Theimplant of claim 24 wherein the first and second sidewalls of the socketare substantially perpendicular to the first plate.
 30. The implant ofclaim 24 wherein the third end wall and the fourth end wall aresubstantially perpendicular to the second plate.
 31. An intervertebralimplant comprising: a pair of first plates adapted to mate to a firstvertebral body, and each of the first plates including an elongatedsocket; a pair of second plates adapted to mate to a second vertebralbody, the each of the second plates including an elongated ball, withthe elongated ball of each the second plates having a top surface andfirst and second elongated sidewalls that are substantiallyperpendicular to the respective second plates, and each the elongatedball having third and fourth end walls; and the top surface of each theelongated ball slopes from the third end wall to the fourth end wall.32. The implant of claim 31 wherein: each the third end wall has aheight that is greater than a height of each the fourth end wall. 33.The implant of claim 31 wherein: each the elongated socket has first andsecond elongated sidewalls, an end wall, and an open end.
 34. Theimplant of claim 31 including at least one of the pair of first platesand the pair of second plates including a keel extending from each theplate and which keel is adapted to engage a vertebral body.
 35. Theimplant of claim 31 including a first keel extending from each plate ofthe pair of first plates and adapted to engage a first vertebral body,and a second keel extending from each plate of the pair of second platesand adapted to engage a second vertebral body.
 36. The implant of claim31 including a first keel extending from each plate of the pair of firstplates and substantially perpendicular to the elongated socket andadapted to engage a first vertebral body, and a second keel extendingfrom each plate of the pair of second plates and substantiallyperpendicular to the elongated ball and adapted to engage a secondvertebral body.
 37. The implant of claim 31 wherein the first and secondsidewalls of the elongated socket are substantially perpendicular to thefirst plate.
 38. The implant of claim 31 wherein the third end wall andthe fourth end wall are substantially perpendicular to the second plate.39. The implant of claim 31 wherein the third end walls of each of theelongated balls are adjacent each other.
 40. The implant of claim 32wherein the third end walls of each of the elongated balls are adjacenteach other.
 41. An intervertebral implant comprising: a pair of firstplates adapted to mate to a first vertebral body, and each of the firstplates including an elongated socket; a pair of second plates adapted tomate to a second vertebral body, the each of the second plates includingan elongated ball, with the elongated ball of each the second plateshaving a top surface and first and second elongated sidewalls, and eachthe elongated ball having third and fourth end walls; and the topsurface of each the elongated ball slopes from the third end wall to thefourth end wall.
 42. The implant of claim 41 wherein: each the third endwall has a height that is greater than a height of each the fourth endwall.
 43. The implant of claim 41 wherein: each the elongated socket hasfirst and second elongated sidewalls, an end wall, and an open end. 44.The implant of claim 41 including at least one of the pair of firstplates and the pair of second plates including a keel extending fromeach the plate and which keel is adapted to engage a vertebral body. 45.The implant of claim 41 including a first keel extending from each plateof the pair of first plates and adapted to engage a first vertebralbody, and a second keel extending from each plate of the pair of secondplates and adapted to engage a second vertebral body.
 46. The implant ofclaim 41 including a first keel extending from each plate of the pair offirst plates and substantially perpendicular to the elongated socket andadapted to engage a first vertebral body, and a second keel extendingfrom each plate of the pair of second plates and substantiallyperpendicular to the elongated ball and adapted to engage a secondvertebral body.
 47. The implant of claim 41 wherein the first and secondsidewalls of the elongated socket are substantially perpendicular to thefirst plate.
 48. The implant of claim 41 wherein the third end wall andthe fourth end wall are substantially perpendicular to the second plate.49. The implant of claim 41 wherein the third end walls of each of theelongated balls are adjacent each other.
 50. The implant of claim 42wherein the third end walls of each of the elongated balls are adjacenteach other.
 51. An intervertebral implant comprising: a first platehaving a socket formed thereon; and a second plate having a ball formedthereon, wherein the ball has first and second sidewalls that aresubstantially perpendicular to a surface of the second plate.
 52. Theintervertebral implant of claim 51 wherein the ball has an upper surfacethat slopes from a first sidewall to a second sidewall.
 53. Theintervertebral implant of claim 51 wherein: the ball is elongated andhas an upper surface that slopes from a first sidewall to a secondsidewall, with the first sidewall having an effective height greaterthan the second sidewall.
 54. The intervertebral implant of claim 51wherein the ball has an upper surface that slopes from a center locationto each of the first sidewall and the second sidewall.
 55. Theintervertebral implant of claim 51 wherein the socket has threesidewalls and an open end.
 56. The intervertebral implant of claim 51wherein the first plate has a keel.
 57. The intervertebral implant ofclaim 51 wherein: the wall is elongated and has an upper surface thatslopes from a center location to the first sidewall and to the secondsidewall with the center location having a height that is greater thanthe height of the first sidewall and greater than the height of thesecond sidewall.
 58. The intervertebral implant of claim 51 wherein thesecond plate has a keel.
 59. The intervertebral implant of claim 51wherein the first plate has at least one keel and the second plate hasat least one keel and further wherein the keels are aligned in parallelplanes.
 60. The intervertebral implant of claim 55 wherein the keel hasteeth.
 61. The intervertebral implant of claim 58 wherein the keel hasteeth.
 62. The intervertebral implant of claim 59 wherein the keels haveteeth.
 63. The intervertebral implant of claim 51 wherein the firstplate has a protrusion on a side opposite the socket.
 64. Theintervertebral implant of claim 51 wherein the second plate has aprotrusion on a side opposite the ball.
 65. The intervertebral implantof claim 63 wherein the protrusion has a profile of a right triangle.66. The intervertebral implant of claim 64 wherein the protrusion has aprofile of a right triangle.
 67. The intervertebral implant of claim 51wherein the second plate has a channel.
 68. The intervertebral implantof claim 67 wherein the channel is formed adjacent the ball.
 69. Theintervertebral implant of claim 67 wherein the channel is formedadjacent the ball on three sides of the ball.
 70. The intervertebralimplant of claim 51 wherein the implant allows movement in a firstdirection and prevents movement in a second direction perpendicular tothe first direction.
 71. The intervertebral implant of claim 51 whereinthe first plate has a protuberance.
 72. The intervertebral implant ofclaim 51 wherein the first plate has a protuberance adjacent the socket.73. The intervertebral implant of claim 72 wherein the protuberance isadjacent the socket on three sides.
 74. The intervertebral implant ofclaim 51 wherein the socket walls are perpendicular to a surface of thefirst plate.
 75. The intervertebral implant of claim 51 wherein thesocket walls are not perpendicular to a surface of the first plate. 76.The intervertebral implant of claim 51 wherein the implant is implantedbetween a pair of vertebral bodies.
 77. The intervertebral implant ofclaim 76 wherein the vertebral bodies are accessed anteriorly.
 78. Theintervertebral implant of claim 76 wherein the vertebral bodies areaccessed posteriorly.
 79. The intervertebral implant of claim 78 whereinthe implant further comprises a pair of first plates and second plates.80. The intervertebral implant of claim 79 wherein the pair of first andsecond plates is implanted such that there is a medial gap between eachof the first plates and second plates.
 81. The intervertebral implant ofclaim 79 wherein the pair of first plates and second plates is implantedsuch that the each of the first plates and second plates abut eachother.
 82. An intervertebral implant comprising: a first plate having asocket formed thereon; and a second plate having a ball formed thereon,wherein the ball has a top that slopes from a first side to a secondside and sidewalls perpendicular to a surface of the second plate. 83.The intervertebral implant of claim 82 wherein the socket has threesidewalls and an open end.
 84. The intervertebral implant of claim 82wherein the first plate has a keel.
 85. The intervertebral implant ofclaim 82 wherein the second plate has a keel.
 86. The intervertebralimplant of claim 82 wherein the first plate has at least one keel andthe second plate has at least one keel and further wherein the keels arenot in the same plane.
 87. The intervertebral implant of claim 84wherein the keel has teeth.
 88. The intervertebral implant of claim 85wherein the keel has teeth.
 89. The intervertebral implant of claim 86wherein the keels have teeth.
 90. The intervertebral implant of claim 82wherein the first plate has a protrusion.
 91. The intervertebral implantof claim 82 wherein the second plate has a protrusion.
 92. Theintervertebral implant of claim 90 wherein the protrusion has a profileof a right triangle.
 93. The intervertebral implant of claim 91 whereinthe protrusion has a profile of a right triangle.
 94. The intervertebralimplant of claim 82 wherein the second plate has a channel.
 95. Theintervertebral implant of claim 94 wherein the channel is formedadjacent the ball.
 96. The intervertebral implant of claim 94 whereinthe channel is formed adjacent the ball on three sides of the ball. 97.The intervertebral implant of claim 92 wherein the implant allowsmovement in a first direction and prevents movement in a seconddirection perpendicular to the first direction.
 98. The intervertebralimplant of claim 92 wherein the first plate has a ridge.
 99. Theintervertebral implant of claim 92 wherein the first plate has a ridgeadjacent the socket.
 100. The intervertebral implant of claim 89 whereinthe ridge is adjacent the socket on three sides.
 101. The intervertebralimplant of claim 92 wherein the socket walls are perpendicular to asurface of the first plate.
 102. The intervertebral implant of claim 92wherein the socket walls are not perpendicular to a surface of the firstplate.
 103. The intervertebral implant of claim 92 wherein the vertebralbodies are accessed anteriorly.
 104. The intervertebral implant of claim92 wherein the vertebral bodies are accessed posteriorly.
 105. Theintervertebral implant of claim 104 wherein the implant furthercomprises a pair of first plates and second plates.
 106. Theintervertebral implant of claim 104 wherein the pair of first plates andsecond plates is implanted such that there is a medial gap between eachof the first plates and the second plates.
 107. The intervertebralimplant of claim 104 wherein the pair of first plates and second platesis implanted such that each of the first plates and second plates abuteach other.
 108. An intervertebral implant comprising: a first platehaving a socket formed thereon; and a second plate having a ball formedthereon, wherein the socket has three walls and an open end.
 109. Theintervertebral implant of claim 108 wherein the first plate has a keel.110. The intervertebral implant of claim 108 wherein the second platehas a keel.
 111. The intervertebral implant of claim 108 wherein thefirst plate has at least one keel and the second plate has at least onekeel and further wherein the keel of the first plates are aligned in aplane parallel to the keel of the second plate.
 112. The intervertebralimplant of claim 109 wherein the keel has teeth.
 113. The intervertebralimplant of claim 110 wherein the keel has teeth.
 114. The intervertebralimplant of claim 111 wherein the keels have teeth.
 115. Theintervertebral implant of claim 108 wherein the first plate has aprotrusion.
 116. The intervertebral implant of claim 108 wherein thesecond plate has a protrusion.
 117. The intervertebral implant of claim115 wherein the protrusion has a profile of a right triangle.
 118. Theintervertebral implant of claim 110 wherein the protrusion has a profileof a right triangle.
 119. The intervertebral implant of claim 108wherein the second plate has a channel.
 120. The intervertebral implantof claim 119 wherein the channel is formed adjacent the ball.
 121. Theintervertebral implant of claim 119 wherein the channel is formedadjacent the ball on three sides of the ball.
 122. The intervertebralimplant of claim 108 wherein the implant allows movement in a firstdirection and prevents movement in a second direction perpendicular tothe first direction.
 123. The intervertebral implant of claim 108wherein the first plate has a ridge.
 124. The intervertebral implant ofclaim 108 wherein the first plate has a ridge adjacent the socket. 125.The intervertebral implant of claim 125 wherein the ridge is adjacentthe socket on three sides.
 126. The intervertebral implant of claim 108wherein the socket walls are perpendicular to a surface of the firstplate.
 127. The intervertebral implant of claim 108 wherein the socketwalls are not perpendicular to a surface of the first plate.
 128. Theintervertebral implant of claim 108 wherein the vertebral bodies areaccessed posteriorly.
 129. The intervertebral implant of claim 128wherein the implant further comprises a pair of first plates and secondplates.
 130. The intervertebral implant of claim 129 wherein the pair offirst plates and second plates is implanted such that there is a medialgap between the first plates and second plates.
 131. The intervertebralimplant of claim 129 wherein the pair of first plates and second platesis implanted such that the pair of first plates and pair of secondplates abut each other.
 132. An intervertebral implant comprising: afirst plate having a socket formed thereon; and a second plate having aball formed thereon, wherein the second plate has a channel.
 133. Theintervertebral implant of claim 132 wherein the socket has three wallsand an open end.
 134. The intervertebral implant of claim 132 whereinthe first plate has a keel.
 135. The intervertebral implant of claim 132wherein the second plate has a keel.
 136. The intervertebral implant ofclaim 132 wherein the first plate has a keel and the second plate has akeel and further wherein the keels are not in the same plane.
 137. Theintervertebral implant of claim 134 wherein the keel has teeth.
 138. Theintervertebral implant of claim 135 wherein the keel has teeth.
 139. Theintervertebral implant of claim 136 wherein the keels have teeth. 140.The intervertebral implant of claim 132 wherein the first plate has aprotrusion.
 141. The intervertebral implant of claim 132 wherein thesecond plate has a protrusion.
 142. The intervertebral implant of claim140 wherein the protrusion has a profile of a right triangle.
 143. Theintervertebral implant of claim 141 wherein the protrusion has a profileof a right triangle.
 144. The intervertebral implant of claim 132wherein the channel is formed adjacent the ball.
 145. The intervertebralimplant of claim 132 wherein the channel is formed adjacent the ball onthree sides of the ball.
 146. The intervertebral implant of claim 132wherein the implant allows movement in a first direction and preventsmovement in a second direction perpendicular to the first direction.147. The intervertebral implant of claim 132 wherein the first plate hasa ridge.
 148. The intervertebral implant of claim 132 wherein the firstplate has a ridge adjacent the socket.
 149. The intervertebral implantof claim 148 wherein the ridge is adjacent the socket on three sides.150. The intervertebral implant of claim 132 wherein the socket wallsare perpendicular to a surface of the first plate.
 151. Theintervertebral implant of claim 132 wherein the socket walls are notperpendicular to a surface of the first plate.
 152. The intervertebralimplant of claim 132 wherein the ball has an upper surface that slopesfrom a first side laterally to a second side.
 153. The intervertebralimplant of claim 132 wherein the ball has an upper surface that slopesfrom a center laterally to each of a first side and a second side. 154.The intervertebral implant of claim 132 wherein the implant is implantedbetween a pair of vertebral bodies.
 155. The intervertebral implant ofclaim 154 wherein the vertebral bodies are accessed anteriorly.
 156. Theintervertebral implant of claim 154 wherein the vertebral bodies areaccessed posteriorly.
 157. The intervertebral implant of claim 160wherein the implant further comprises a pair of first plates and secondplates.
 158. The intervertebral implant of claim 160 wherein the pair offirst plates and second plates is implanted such that there is a medialgap between each of the plates of the pair of first plates and secondplates.
 159. The intervertebral implant of claim 160 wherein the pair offirst plates and second plates is implanted such that each of the platesof the pair of first plates and second plates abut each other.
 160. Anintervertebral implant with an upper plate and a lower plate having: aforward bending movement of ten degrees; a rearward bending movement offive degrees; a right lateral bending movement of five degrees; a leftlateral bending movement of five degrees; a right axial rotation ofthree degrees; a left axial rotation of three degrees; and an inhibitionof forward to rearward movement between the upper plate and the lowerplate.